1. Field of the Invention
This invention relates to a view finder, more particularly to a view finder which is suitable to be used for a camera.
2. Description of the Related Art
A conventional view finder used for an auto-focus camera has an observation optical system and indicating frames. One of the indicating frames is a field frame used for indicating a photographing field of the camera. The other indicating frame is a distance measuring frame used to indicate a distance measuring zone measuring a distance of an object, by the distance measuring device provided in the camera.
The conventional view finder is arranged so that both the indicating frames and an image of the object seen through the view finder are superimposed so that the observer can clearly visualize them.
As for an inverted Galilean type alvada finder which is a well-known view finder, a transparent plate, forming reflection patterns corresponding to the indicating frames thereon, is disposed in front of an eyepiece lens, as viewed from the observation optical system side. The pattern is reflected by a luminous flux passed through the finder. Both the reflected pattern and the image of the object are observed through the eyepiece lens.
As for an inverted Galilean type finder of the light intake type, a pattern plate having transparent portions (or notch portions) corresponding to the indicating frames is illuminated by external light, the transparent light, which passed through the pattern plate, and the image of the object are superimposed by a half mirror, so that the observer can observe both the indicating frames and the image of the object.
On the other hand, in a real image type view finder, the transparent plate, having patterns corresponding to the indicating frames, is provided at a predetermined position which coincides with a position where the real image of the object, located at a specific distance, is formed by an objective optical system. Hence, the observer can observe both the indicating frames and the real image of the object formed on the transparent plate. However, the conventional view finder, as described above, has had several problems. The ability to easily see the indicating frames depends on the background view of the picture to be photographed and the brightness of the object, in other words, it is not easy for the observer to recognize the indicating frames when the photographing scope is dark. In addition, since the distance measuring frame is only a partial outline of the distance measuring zone, so as not to disturb his or her sight in the view finder, it is not easy to recognize the distance measuring frame in particular. Furthermore, an imaging position of the virtual image or the real image of the object, which is formed by the objective optical system, varies in the optical axis direction of the objective optical system, according to the objective distance of the object.
Therefore, when the observer observes the image of the object, the observer will unconsciously adjust the focus of his or her eye corresponding to the variation of the imaging position. Hence, the observer can clearly see both the image of the object and the indicating frames when the imaging position substantially coincides with the predetermined position at which the plate is disposed. Although in most cases, namely, when it does not coincide with the predetermined position, the observer is forced to alternate the focus of his or her eye. This causes fatigue in the observer's eye.